1. Field of the Invention
The present invention relates to a gas spring device, and more particularly to an improved gas spring which improves the quality of a speed reducing device.
2. Description of the Prior Art
A gas spring device used in a copier, a vehicle, an industrial device includes a cylindrical chamber having one end closed by a tape holder closed by a flange, a gas seal, and an open holder. The gas cylinder device includes a speed reducing device so that a gas in the cylinder chamber is passed through an axial recess, slidably moving a region of the cylinder chamber. The gas cylinder includes a piston rod having one end connected to the speed reducing device and the other end penetrated through the flange, the gas seal, and the open holder and located outside the cylinder chamber.
Since the gas in the cylinder chamber is higher than the atmospheric pressure, a force which pushes out the piston rod in the chamber and the piston rod is protruded outside.
If the protruded piston rod is pushed inside of the chamber with a force higher than the gas pressure in the chamber, the chamber is separated to two regions and the gas is moved from the chamber having a high pressure to the chamber having a low pressure along the axial recess formed in the speed reducing device.
The gas in the chamber is moved faster when the piston rod is pushed towards into the chamber. The gas in the chamber is moved slower when the pushed piston rod is moved to the original position so that the piston rod is slowly restored.
A speed reducing device of a conventional gas spring is disclosed in Korean Patent No. 84-1891, which will be in detain with reference to FIGS. 2, 3a, and 3b. 
FIG. 2 is a cross-section for showing a conventional gas spring device. FIGS. 3a and 3b is a top view for showing a conventional piston. FIG. 3b is a rear view for showing the conventional piston.
The conventional speed reducing device 50 is slidably moved along the inner wall surface of the cylinder 10 As the piston is moved. The speed reducing device comprises a piston 20, upper and under washers 5 and 6 which sandwich the piston. A Teflon(copyright) (Teflon(copyright), as used throughout the specification is a registered trademark, and is a synthetic fluorine containing polymer) ring 7 which is mounted to an annular recess 40 formed by the under washer 6 and the piston 20, and an axial recess 8 which penetrates the piston 20.
If the speed reducing device 50 is assumed to move along the A direction, the TEFLON ring 7 is moved towards the upper washer 5 by the friction with the inner wall surface of the cylinder and blocks apertures 30a and 30b through which the gas between the piston 20 and the cylinder 10 is moved. The axial recess is connected to a gas inlet and outlet 8b through a gas passage 8c formed on the upper surface, and is connected to a gas inlet and outlet 8a through a gas passage 8d. The gas inlet and outlets 8a and 8b are always opened so that the gas in the cylinder chamber separated by the speed reducing device is passed to each other. The movement of the gas through the gas inlet and outlets 8a and 8b enlarges the resistance of the flow of the gas and damps the gas flowing speed. The damping degree can be regulated by the number of the axial recess 9 formed along the gas passage 8c and 8d. 
Namely, since the TEFLON 7 blocks the apertures 30a and 30b through which the gas between the piston 20 and the cylinder 10 is moved, the gas is moved only through the axial recess 8 and the gas inlet and outlet 8a and 8b to damp the moving speed of the speed reducing device 50 moved towards A direction. The outer diameter of the upper washer 5 is equal to or smaller than the outer diameter of the piston 20. A cutting portion 6a having a size sufficient to pass the gas passing the apertures 30a and 30b is formed in the under washer.
On the other end, if the speed reducing device 50 is moved in the opposite direction of A, the TEFLON ring 7 is moved towards the under washer 6 by the friction with the inner wall surface of the cylinder 10 to open the apertures 30a and 30b between the piston 20 and the cylinder 10. If the TEFLON ring 7 is moved towards the under washer 6, the inner peripheral surface of the TEFLON ring is located in a region of the cutting portion 6a and the gas which moves along the apertures 30a and 30b is easily moved through the cutting portion 6a. Then, since the axial recess 8 is opened, the gas is moved from the gas inlet and outlet 8b to the gas inlet and outlet 8a. 
If the apertures 30a and 30b between the cylinder 10 and the piston 20 and the axial recess 8 formed so as to penetrate the piston 20, the function of the speed reducing device is not accomplished.
Another pattern of the gas passage 8c and 8d is disclosed in U.S. Pat. No. 4,438,833, which is shown in FIG. 4.
In the structure of FIG. 4, a gas passage 8c is spirally formed to delay the flow of a gas.
The piston of the speed reducing device having the above-mentioned structure has a width of the aperture which has a predetermined value to move the gas much through the apertures 30a and 30b to reduce the damping reaction of the gas. Further, since the shaking between the piston 20 and the cylinder 10 is severe due to the aperture, the preciseness of the gas shielding due to the Teflon ring is deteriorated and the speed damping preciseness of the gas flow is lowered.
Further, since the gas passages 8c and 8d formed on the surface and the rear surface of the piston is curved or spirally formed, the piston cannot be easily manufactured by the cutting.
The present invention has been made to solve the above mentioned problem, and accordingly it is an object of the present invention to provide a gas spring device which can improve the quality of a speed reducing device.
In order to achieve the above-mentioned object, the present invention provides a gas spring device which forms a chamber which is filled with a gas at a pressure higher than the atmospheric pressure by closing both ends and includes a piston rod extended towards the inside and the outside of the chamber though one of the both ends of the chamber and a speed reducing device fixed to an end of the piston rod located in the inner side of the chamber to separate the chamber into two spaces through which the filled gas is slowly moved, wherein the speed reducing device includes an uneven piston, an under washer and an upper washer which make contact with upper and lower surfaces of the piston, and a TEFLON ring mounted to an annular recess formed between the piston and the under washer and having an outer peripheral surface adhered to the inner wall surface of the cylinder and an inner peripheral surface separated from the bottom surface of the annular recess, at least one cutting recess formed on the outer peripheral surface of the piston located between the TEFLON ring and the upper washer, at least one speed reducing gas passage formed on the upper and lower surface of the piston, and at least one axial recess penetrating the piston so that the gas passage of the upper and lower surfaces of the piston.
The piston, the piston, the upper washer, the under washer are penetrated and fixed by the piston rod, and the axial recess is formed along a penetrating recess surface of the piston. The under washer has a cross shape.
The Teflon has a circular shape and a portion of the circular shape is cut off.
The piston is comprised one selected from a metal material, a nonmetal material, and a resin material.